There's about 0.004" to 0.005+" difference between the minimum chamber headspace for a go gage and the point just before the bolt closes on a no-go gage.

So there's room to work.

And as I indicated above, there's more than one way to arrive at the proper headspace. The headspace issue is widely misunderstood by many shooters. At the very crux of the issue, headspace is just the distance from the datum for the cartridge in question to the bolt face. For the .30-06 and similar non-magnum, bottlenecked cartridges, the datum is a point on the shoulder. For a belted magnum, the datum is on the front of the belt. For a rimmed cartridge (eg, .30-30), the datum is on the front of the rim, etc.

Nitriding: The nitriding processes I've seen used on barrels have been salt baths.